Greg Eagles was the voice of The Grim Reaper and Sperg, Greg has appeared in other shows and some video games, but Grim is his most memorable performance
Grey DeLisle was the voice of mandy.and she has also been in alot of other shows such as Rugrats,Johny Bravo, wild Thornberrys, the list goes on and on.
Richard Steven Horvits was the voice of both Billy and his dad, he is also the voice of many mentaly unstable characters in tv, such as Zim from Invader Zim.
Irwin was voiced by Vanessa Marshal,she has also done work for Fishhooks and additional voices for Rogue one
Jennifer Hale was the voice of Billys mom,she has also worked on Rick and Morty, Dexters Laboritory, Johny Bravo and lots of others
The show also had several guest stars voice characters, people such as
Gilbert Gottfriedm,a well know comedian and actor who has been in many movies and tv shows. well known as the voic of Iago from Alladin.
Carol Kane, an occomplished actress who has been in films such as Scrooged and tv serires like Gotham
Malcolme McDowell, well known voice actor who has voiced characters in movies like Bolt and shows like Southpark
R. Lee Ermey, a well known actor, voice actor and marin, Most known for his role in the film Full Metal Jacket
Frank Welker a known voice actor who has done work for the Simpsions, Ducktales and Tom and Jerry
Weird Al Yankovic, a famouse parody and comedy song writer and actor